The fact that long-chain polyisoprenoid alcohols serve as intermediates in transglycosylation reactions is now well-established. The extent to which these intermediates participate in glycoprotein glycosylation, whether generally, or for a limited number of specific glycoproteins, is not known at present. The physiological significance of the glycoproteins makes it important to understand the means by which these compounds are synthesized. In animal tissues the class of compounds which serve as glycosyl donors has an average chain length of 95 carbons and the isoprene unit bearing the hydroxyl is saturated. This class of compounds is called dolichol. Radioactive dolichol has been prepared with a very high specific activity and the tissue and subcellular distribution has been determined following injection into rats. Dolichol is rapidly incorporated into the high density lipoproteins following intravenous administration. The labeled material circulates with a half-life of about 10 hours and is accumulated mainly by the liver; the bulk of the radioactivity in the liver is localized in the outer mitochondrial membrane. The means by which this localization is achieved and the reactions involving dolichol are now under investigation.